Prior art devices including optical reflection sensors with background suppression or distance measuring devices generally make use of the triangulation principle described by FIG. 1. Beyond a maximum distance, the operation of the sensor is impaired due to the fact that the angular sensitivity decreases with the distance. When attempting to increase this distance, the result is an enlargement of the dead zone which excludes an operation in the proximity of the sensor.
In order to adapt this limited measuring range to varying situations, certain manufacturers use an adjustable mirror that allows the best adaptation of the measuring range. Such a solution is e.g. described in U.S. Pat. No. 3,759,614.
Other solutions are known as well: Different references such as GB-A-2 069 286 and DE-A-196 19 308 suggest a pulsed emission and an analysis of two receiver channels. DE-A-24 55 733 alternatingly uses two lighting optics located in the same plane. DE-C-40 04 530, DE-C-40 40 225, DE-C-41 40 614 as well as DE-C-198 08 215 suggest that a plurality of alternatingly emitting light sources are provided in the same optical channel. The receiver channel is formed by multiple detectors or by a position-sensitive detector, e.g. PSD, the electronic circuit being capable of processing the signals corresponding to each one of the light sources to obtain information concerning the distance to the target. A sophisticated treatment of this information allows a slight extension of the range of the measuring system.
However, the inherent limitations of the principle of triangulation between elements that are situated in the same plane as defined by the optical axes of the emitting and receiving systems do not allow a substantial improvement of the performance with respect to distance, linearity, and the dead zone. Thus, in the case of a measuring sensor or of a background suppression triangulation sensor, a calculation of the ratio between the maximum detection distance and the minimum distance of the measuring range yields a quality number that is rarely greater than 5. On the other hand, such detectors are very often sensitive to the amount of light reflected by the target, which depends on the texture and the color of the latter.
On the background of this prior art, a first object of the present invention consists in substantially improving the results of measurements by triangulation without the need for complex analyzing circuits. This is accomplished by an optical distance detecting or measuring device wherein said device comprises at least a second detector that is aligned with the first detector on an axis contained in a plane that is inclined at an angle with respect to the reference plane, said angle being comprised between 10° and 170°.
A second object is to allow the realization of efficient measuring or background suppression sensors having small dimensions. This is accomplished by an optical distance detecting or measuring device, comprising a light source and receivers, wherein the light source emits light pulses of different intensities that are intended alternatingly for each one of said receivers, the emitted intensities being regulated in such a manner as to produce signals having identical amplitudes or corresponding to a predetermined function on the receivers, and an optical distance detecting or measuring device, comprising a sensor with a single lens including distinct emitting and receiving sectors, each sector being provided with a prism for focusing the light beams on the emitting and the receiving elements, respectively.